In order to supply power to a power grid, an electric energy generating machine, in particular a plurality of electric energy generating machines such as a plurality of wind turbines in a wind park or a plurality of solar photovoltaic machines in a solar plant, controlled by a centralized plant controller, needs to conform to certain requirements. For example, the electric energy generating machine may need to offer the capability to remain on-line and continue to produce power during high-voltage conditions on the connected transmission or distribution system. This can be described as a high voltage ride through (HVRT) capability. HVRT capability would require that the electric energy generating machine remain connected to the power grid during a high voltage condition to enhance the stability of the grid.
EP 2 209 205 A1 discloses a method for operating a wind power plant with a rotor-driven electric generator for delivering electric power to an electric grid which provides a grid voltage. The method includes that, when excess voltage prevails in the grid, idle or reactive power from the wind power plant is fed to the grid in order to lower the voltage and that a monitoring occurs to determine whether a voltage was lowered within a predeterminable time to a predeterminable reference value and/or an idle or reactive current is delivered which is greater than or equal to a predeterminable idle current reference value. However, this scheme makes no provisions to adjust active power production to release reactive capability of the wind turbines. Additionally, this disclosed method applies exclusively to rotor-driven wind turbines with available reactive current. This method also requires a considerable amount of analysis to establish the necessary predeterminable values, which may vary from site to site.
There may be a need for a simple, effective, and efficient voltage regulation during high voltage conditions, using a central plant controller.